Portland Cement Pastes Influence of Composition on Volume

October, 1934

I N D U S T R I A L .\ N D E S G I N E E R I K G C H E M I S T R Y

lead carbonate content from 67.1 to 79.5 per cent. After 12 months of exposure, indications are that the durability of the paint film is practically the same, whether niade of white lead of high or low lead carbonate content. SUMMARY

As the chemical structure of electrolytic whlte lead varied, the physical properties varied also. As the k a d carbonate content of the pigment increased, the physical properties, such as tinting strength, (Consistency,oil absorption, etc., decreased. Electrolytic white leads of varying chemical structure are made to meet desired physical properties. Electrolytic white leads other than those of the theoretical constitution 2PbC03.Pb(OH), are used to advantage by the paint trade.

1019

LITERATURE CITED (1) Am. SOC. Testing Materials, Standards, Pt. 11, p. 534, specification D81-31 (1933). (2) Green, H., J. Franklin Inst., 192, 637 (1921). (3) Heaton, S . , “Outlines of Paint Technology,” p. 66, Charles Griffen & Co., London, 1928. (4) Lambert, T . , “Lead and Its Compounds,” p. 36, Scott, Greenwood & Son, London, 1902. ( 5 ) Martin, “Industrial Chemistry,” 6th ed., p. 497, Crosby, Lockxood & Sons, London, 1922. (6) Stutz and Pfund, ISD. ENG.CHEM.,19,51-3 (1927). (7) Thorpe, “Industrial Chemistry,” 3rd ed., p. 222, Longmans. Green 8: Co., London and Kew York, 1916. RECEIVED M a y 15, 1934. Presented before the Twelfth Ivfldwest Regional Meeting ot the American Chemical Society. Kansas City, Mo., M a y 3 to 5 , 1934.

Portland Cement Pastes Influence of Composition on Volume Constancy and Salt Resistance R. H. BOGUE, WILLIAMLERCH,AKD W‘. C. TAYLOR Portland Cement Association Fellowship, National Bureau of Standards, Washington, D. C.

T

HE problem of the volume constancy and salt resist-

This paper presents the results obtained in a number of investigations which indicate ihe effects of cement composition on the aolume changes of pastes stored in water and air and on their resistance to the action of .solutions containing salts which m a y be encountered in natural waters. Volume changes are considered from the viewpoint of hydration, colloidal swelling, and the formation of secondary products. Salt action is considered f r o m the viewpoint of the .formation of addition products and reactions of base exchange.

ance of concrete is complex and involves many variables, one of which is the comp o s i t i o n of the cement used. It is the purpose of this paper t o b r i n g t o g e t h e r data that have been obtained c o v e r i n g the effects of cement composition on the v o l u m e c h a n g e s of pastes stored in water and air and on their resistance to the action of sohtions Containing salts which may be enc o u n t e r e d in natural waters. The results reported have been taken from data accumulated over a period of years in a number of investigations. For purposes of reference the series designations are given, but, inasmuch as the conditions have varied in different studies, the results reported from the different series are not usually quantitatively comparable.

EXPERIMENTAL PROCEDURE The laboratory cements listed as members of series C-8 and C-9 were prepared from c . P. chemicals in an up-draft, gas-fired kiln in the manner described in a previous paper (16). The temperature and time of heating were such that essentially complete combination was effected, as determined by the ammonium acetate test for free lime (IC), except as especially noted. The clinkers mere ground in a pebble mill to such fineness that approximately 86 er cent passed a No. 200 sieve. A chemically pure gypsum, 8aSOc 2H20, was incorporated in the ground clinkers in such quantity as to give the sulfur trioxide contents specified. Except where otherwise stated, the specimens for the volume change measurements were prepared within a few days after grinding. The specimens of series C-8 were of 1 : 2 and 1: 4 mortars; those of series C-9 rere neat. The cements given under series K-B-7 and K-2 were prepared from commercial raw materials and burned in an experimental rotary kiln. The clinkers were ground to a fineness of 87.5 =t 0.5 per cent passing the No. 200 sieve, following the addition of gypsum to give 1.8 per cent sulfur trioxide in the cements. In these series the specimens stored in water were prepared of neat pastes and, for all other exposures, of 1 : 2 mortar.

The compounds were computed

by the method described by one of the authors in an earlier paper (6).

For the preparation of the neat cement specimens, water was added to produce a paste of normal consistency ( 2 ) . For the preparation of the mortars the water added was calculated from that required to produce normal consistency by use of Feret’s consistency formula (cf. Johnson, 11):

“L) + h‘ 3 n+l

y

Khere Y

=

yo water required for the mortar

P = % water required for neat cement (normal consist-

ency) n = parts of sand for 1 part cement K = constant, 6.5 for standard Ottawa sand Standard Ottawa sand was used. Bars for length measurements were cast in a brass mold, 13 inches long, 1 inch wide, and 1 inch deep. In order to reduce the restraint on the specimens during setting and early hardening, a block of sponge rubber, 1 inch thick, was placed at the middle of the mold, permitting two &inch specimens to be cast in each mold. When the specimens had attained an initial set, the catch on the mold was loosened as a further means of decreasing restriction to movement. When the specimens were being cast, glass plates were countersunk in each end of the bar, and a capillary tube was inserted vertically in the paste about 0.5 inch from each end. The specimens and mold were then covered with a glass plate containing 1-inch holes over the capillaries. The glass plate was greased with vaseline at the area of contact with the mold, and the holes in the plate were covered n-ith small glass plates. In this manner evaporation of water from the specimen during the time it was in the mold m s reduced to a minimum. During the first 24 hours the temperature of the specimens was maintained a t about 20” to 25’ C. (68’ to 77’ F.), and the length measurements were made with an invar microscope comparator reading to 0.001 mm., by focusing the microscopes on the capillary tubes in the specimen. The molds were then removed, and subsequent over-all length measurements were made by the use of an invar micrometer graduated to 0.001 mm. Upon removal from the mold the specimens were placed in water for 6 days. For the subsequent period different groups of specimens of series

1050

INDUSTRIAL A N D ENGINEERIIVG

C 8 and K-2 were stored in water, in 2 per cent sodium sulfate

solution, in 2 per cent magnesium sulfate solution, and in air of about 45 per cent relative humidity. The specimens of series C-9 were stored in water, in air, and alternately in water and air for 7-day intervals, The water bath and air cabinet were maintained at 25" C. (77' F.). In some of the studies (series (2-8)designed to observe the effect of composition on resistance to sulfate and other salt solutions, 1-inch mortar cubes were prepared of 1: 2 and 1 : 4 mixes by weight, using standard Ottawa sand. The amount of water used was that required to give a plastic mortar. These specimens were cured in water for 28 days, following which different groups were placed in water, 3 per cent sodium chloride,

Vol. 26, No. 10

CHEMISTRY

calcium aluminate to form calcium sulfoaluminate (IS)with a computed increase in volume of solid phase of about 168 per cent. If V h = molecular volume of the hydrated phase and Va = molecular volume of anhydrous phase or phases, the percentage increase in volume of solid phase P is found by solution of the equation:

p = -100 V h - 100 Vu

The molecular volume, V , is found by dividing the molecular weight, M , of a crystalline solid by its density, d:

V = M/d

---

-0.2

---

5-5-5-15

0-10-0-0

8 - 5 % SO,

A - 2 % SO,

WATER

Y

Molecular volumes of a number of cement compounds and their hydration products are given in Table I. Since this increase of 168 per cent is more than twice that resulting from the hydration of the 3CaO.Al2O3 (computed to be 72 per cent), it may be expected that a dependent relation obtains between the volume change in any specimen and the relative quantities of 3Ca0.A1203 and sulfur trioxide that are present. I n these series gypsum was ground with the clinkers to give 0, 2, and 5 per cent sulfur trioxide. Some of the data on neat cement specimens from the group with the sum of alumina and ferric oxide constant are given in Figure 1. Abbreviations in the formulas of the compounds have been used as follows :

STORAGE

o 5-56-15

5-5-5-15

-03

-0.3

-04

-0.4

A =

-05

0 I 2 3

u

5 6 7 8 Q10llIZ/3

G - 2 % so3

52 AIR

ACT

AT

- 0.5 0

A1203

F = FetOa

-

C = CaO Si02 S I 2 3 4 5 6 7 8 9101112IJ

D-5s so3

CsS CIS

= = = =

3CaO.SiOa

2CaO.SiOt 2CaO.FezOs CaA 3CaO*AlaOa C4.4F = 4CaO.Alt03.Fea03

CzF

2

STORAGF TEST IN WCEKS

FIGURE1. CHANGE I N LENGTH OF SPECIMENS IN WHICH FERRICOXIDEIS SUBSTITUTED FOR ALUMIKA

The results obtained on the specimens stored in water are shown in graphs A and B. Two per cent of sulfur trioxide was present in the samples shown in 1A and 5 per cent in the samples of 1B. The percentages of alumina and ferric

2.5 per cent magnesium chloride, 3.1 per cent magnesium sulfate, and 3.6 per cent sodium sulfate solution. In these amounts the salts were present in equivalent molar concentrations. Large tanks were used for storage in each case, and the salt concentrations were maintained essentially constant. The specimens were examined at frequent intervals, and compression tests were made on the cubes at ages of 1, 3, 7, 28 days. 3, 6, and 12 months.

EFFECT OF VARYING THE RATIO OF 3Ca0.A1z03 to 4Ca0.AlzO~Fez03AND THE SULFURTRIOXIDE CONTENT A group of laboratory cements (series C-9) was prepared in which the sum of alumina and ferric oxide was maintained a t 10 per cent while the ratio of alumina to ferric oxide was caused to vary. A second group was prepared in which the alumina content remained constant and the ferric oxide increased while the calcium oxide and silica were adjusted to give a substantially constant computed 3CaO.SiOz content in the clinker. Some of the members of these groups were outside of the composition range of commercial cements but were included in the study in order that the influence of the compounds formed on burning might be more definitely indicated. I n the first group, computations indicated that the 3Ca0..&03 content diminished from 26 to 0 per cent while the 4CaO.Al2O3.FekO3 increased from 0 to 15per cent; and that in one member, 2Ca0.Fe203 was present to the extent of 17 per cent. I n the second group the 3CaO.Al203 decreased from 26 to 10 per cent and the 4CaO.Alz03.Fez03 increased from 0 to 30 per cent, while the alumina remained constant. I n all cases the computed 3CaO.SiOz content was maintained nearly constant at 50 per cent. These arrangements permit of an interpretation of volume changes in terms of either the compounds or the components. I n these groups also a special study was made of the influence of the sulfur trioxide introduced by various amounts of gypsum, Calcium sulfate reacts (solid phase) with tri-

-02

-03 10-0-

D-5% AiR

-

,

so1

STORAGE

FIGURE2. CH.4NGE IN LENGTHOF SPECIMENS IX WHICH FERRICOXIDEINCREASES WITH ALUMINA CONSTANT

oxide in the samples are shown on each curve, followed by the percentages of 3Ca0.A1203 and 4CaO.Al203.FezOa computed from the analyses. It is evident that the expansion of the specimens of this group in water diminishes as the alumina or the 3Ca0.Al2O3is decreased. This condition is pronounced during the reduction in the 3CaO.Al203 from 26 to 5 per cent but is not evident on the further reduction of the 3CaO.Al2O3to zero. I n this series the reduction in alumina content from 10 to 5 per cent results in a computed decrease of 21 per cent in

I N D U S T I\ I A L A N D E N G I N E E H I N G C II E M I S T 13 U

Oclutrr, 1934

3Ca0.A120a and an increase of 15 per cent in 4C:aO.AlzOaFczOa. But the further reduction in alumina from 5 to 0 per cent decreases the 3Ca0.NzOa content only 5 per cent and brings the 4Ca0.Al20gFe2Oaalso to 0 per cent with the substitut.ion of 17 per cent of 2Ca0.Fe20s. The results suggest that the volume changes are determined by the 3CaO.AI1Oa content (or ratio of alumina to ferric oxide) rather than by the percentage of alumina present. Since the 4Ca0~Al9O3~FczO8 content changes in the order of 0, 8, 15, 0 per cent, it appears that the 4CaO-AlzOsFezOsexerts a relatively unimportant effect on the volume changes of the specimens. The contraction of the specimens in air is shown in Figures IC and D. The differences due to the varying 3CaO.Al2Os contcnt are shown to indicate a consistent tendency for the higher 3Ca0.Al1O8 contents to induce the larger contractions. In agreement vith these observations the measurements made on tlie specimens stored alternately in water and in air (not shown in the diagrams) show increasingly large changes as the 3Ca0.A120scontent increases. The results obtained in the group where alumina was maintained constant a t 10 per cent are shown in part in Figure 2. In this group further opportunity is offered to observe whether the volume changes are proportional to t.he total alumina present or to the computed 3CaO.ALOa content (or ratio of alumina to ferric oxide). These results appear to be similar to those of the preceding group and the comments made above apply equally well here. The expansions in water, Figure 2A and B, are shown to be markedly diminished by reductions in 3Ca0.A1*O8from 26 to 15 per cent (the ratio of alumina to ferric hydroxide from infinity to 2) and this takes place while the alumina remains constant and the 4CaO-Al,0,~FeZOH increases from 0 to IS per cent. The contraction of the specimens in air and the magnitude of the variations in alternate storage (not shown) are diminished as the 3Ca0.AlSOsis reduced from 26 to 10 per cent. These data confirm the suggestions, arising from the consideration of the previous series, that the expansion in water and the contraction in air are functions of the 3CaO..4120a content (or the ratio of alumina to ferric oxide), that increascs in 3Ca0.AlzOJ a t the expense of 4Ca0.AlzOa-FezOs result in increased volume changes and that tlie volume changes are not indicated by the total alumina content. The data (not given in the figures) show that an increase in gypmm content from 0 to 2 per cent sulfur trioxide has a relatively slight influence on the length changes in all compositions, But the further increase in gypsum content to 5 per cent sulfur trioxide (as shown in the figures) gives rise to large length increases in the specimens high in 3CaO.ALOa (high ratio of alumina to ferric oxide) stored in water. This

gypsum appears to produce n slight decrease in the contraction of the specinierrsin air. The action of tlie gypsum niay be explained by the following considerations. The calcium sulfate enters into reactiou with the tricalcium aluminate a t a rat,e proportional to that

FTOURE 3. EFFSCTOF Cmxor~o3Ca0.AIsOa CONTENT W7TH ALUMINA AND

GYFBW7

Cdoite Lime Brucite MP.gne*ia Trioslciurn duniinate hydrate Trienlriurn a1uminste Calaiun. sulfoaluminate Cnleiuin chloiosluminate

AND

THEIRHYnnATloli

Ce(OHh CnSO1.2l310 C8COI

74.1 172.2 100.1

MdJ 3CaO-A1.01.ati10 3CsO~AI~Oa :~CaO.Aln01.3CsSO~31&O 3CnO.AInO~CaCI~ lOH-0

378.2 270.1

2.41 2.95

561.3

2.19

c.0

may be noted by a comparison of graphs A and Bin Figures 1 and 2 (note the differcnee in scales). A reduction in the 3Ca0-A1203 content of the cement (or a decrease in the ratio of alumina to ferric oxide) reduces the effect of the added gypsum; and when the 3Ca0-AlaOs (or ratio of alumina to ferric oxide) is low, the increased gypsum has but slight influence on the length changes. The added

3CaO-SiOp CONSTANT

at which those compounds go into solution and precipitate out again as calcium sulfoaluminate. A part of the gypsum may be expected to complete that cycle prior to the initial set, in whicli case i t does not eontributc to subsequent volume changes. The comparativcly slight differences in length change between the mixtures containing 0 and 2 per cent of sulfur trioxide suggest that the greater part of the 2

TABLE I. MOGECULAR V O L U ~OF S CEMEN?COMPOUSDS Calcium hTdroride

1051

6R 1

2 . 2 3 (S) 2 . 3 2 (10) 2.71 (IO) 3 . 4 0 (10)

40.8

2 . 4 0 (IO) 3.65 (10)

1286.9

1.46 ( t S l

PRODUCTS

33.2 74.3 37.0 16.5 24.3 11.0

157 91.6 836 256

per cent of sulfur trioxide has reacted prior to the initial set. Rut the large increase in expansion in water which occurs in the mixtures high in 3Ca0-Al2Oe to which 5 per cent of sulfur trioxide was added, leads to the belief that much of the sulfur trioxide in that case fails to react until after the initial set has taken place. Also it appears probable that, in the semi-rigid structure of these specimcns, the pore

1 N 1) 1: S T I < I A 1.

IlIiZ

A N 1)

il N G I N E E R I N G C 21 E M I S T R Y

Vol. 26, No. 10

content (6 per cent; ratio of ahmiilia to ferric oxide, 1) prepared from the lean mix with high water content (1:4 mix, 40 per cent water hy weight of the cement) are in a much better condition after 6 months than are the specimens of higher 3Ca0.A1203content (I1 and I6 per cent; ratios of alumina to ferric oxide, 2 and infinity) prepared from the rich mix with lower water contcnt (1:2 mix, 26 per cent water). This shows that certain chaiiges in composition (reduction in 3Ca0-AL08 content or ratio of alumina to ferric oxide) may be more effective in improving resistaiice to sulfate action than changes in the richness and water content of the mix. Specimens immersed in solutions of sodium chloride and iriagnesimn chloride shorn no outward signs of disintegration l i p to two years. Tlie results on compressive strength tests obtaiued in the &we gronp of spet:imens show that t,lie compositions high in tricalcirim aluminate (16 and 11 per cents; ratios of alumina to ferric oxide, infinity and 2) are reduced in strength after 6 moiitlis iii the sillfate solutions to a inricli greater degree than is the cement low in :3Ca0-AI20, (6 per cent; ratio of alumina to ferric oxide, I). The specimens immersed in t,he magnesium chloride solution show definite reductions in strength, brit tliose in the sodium chloride solut.ion retairi strengths similar to the specimens stored continuously in water. Typical specimens of tlic 1:2 mortar bars of serius K-2 after immersion in sodium sulfate solutions for 18 niontlis are shown in Figure 4. The compositions of the cements and the percentage expansion, except where tlie specimen had disint,egrated so much as to make nieasrirenients impracticable (indieatad by x) are given. 4 rather sharp line may be drawn in this photograph between those that arc satisfactory after IS months of storage in the sulfate solution and those wliicli liave expanded so miicli as to be approaching a condition of disintegration. The cements containing 7 per cent or less of 3Ca0-Al1O3(ratios of alumina to ferric oxide, 1.3 ti) 0.3) arc in excellent condition; those containing 11 per nzindieatea acuirdiLiunoieroeasiveerpanaion whiohcouidnot herneasurod. cent or more of 3Ca0.AIz0a (ratios of alumina to ferric FIGUHK 4. EFFECT OF VARYING T H E 3CaO.AI.0, CONTENT oxide, 1.9 to 6.4) are in poor condition. 05 LARoRATORY CEMEKTS I\l?nEESI+> IN 2 PER CENT Figure 5 shows the percentage change in length of speciSonim Snrra.rt; So~urrovFOR 18 Momws mens of this series (K-2) over a period of one year. httenspace 111aj absorb a erinsideriLble aiimunt of actual iiicmise tion is directed again to the use of neat specimens for the in total v h n e OS the solid phase hefore the external di- water storage and 1:2 mortar speciinens for all other conditions of storage, and also to the different scales of ordiiiates mensions of tlie specimen are apgrcciahly affected. The effects of tricalciimi aluminate on the resistance to made necessary as a result of the much greater expansions sodioni sulfate and magnesium sulfate solutions at 6 iiionths in the sulfate solutions than in water. It is apparelit from (series C-8) are shorn in Figure 3 where the cornputed these graphs that in all cases the length changes increase 3Ca0.AIIOI and 4CaO~Al2O8~E'eZOa are caused to m r y , and as the computed 3Ca0.AhOa content (or ratio of alumina to alumina mid 3CaO.Si0, a.re held coilstant. The oxide and ferric oxide) of tlie cements increases. Another group of cements in the IC-2 seriea wns designed to calculated compound cornpositions are given and tlie spccimens are shoivn of both I :4 and I :2 mixes. It is i~bservcd give cements of uniform computed 3(>aO.A1& contents that, i n the compositions high in 3CnO.AI& (high ratio while tlie R,O, and 3Ca0-SiOz contents were allomxl to of alumina to ferric oxide), disintegratioii has usually oc- change. The compositions of t.his group arc given in Table curred under the conditions of the experiment. But when 11, together with the expansion in sodium suliate solution the 31'a0.AIrOa content (or the ra.tio of alumina to ferric at 1 year; 1:2 mortars ivere used. ln this series the expansions, being of the same order of oxide) decreases, the conditim of the specimens is showi to riiagnitude throughoiit the group, arc indicated hy the nearly he improved. .knother point